Nowadays, as a two-dimensional code which expresses information data of n bits by a two-dimensional image pattern, various kinds of information codes such as a QR (Quick Response) code are used. In recent years, there has been proposed a coordinates input system in which by making a light pen come into contact with a display screen of a display, a coordinate position in the display screen with which the light pen has been come into contact can be detected (for example, refer to Patent Document 1). In the coordinates input system, two-dimensional codes each showing the coordinate position in the display screen are displayed on the corresponding coordinate positions in a matrix form. In this instance, the light pen photographs a two-dimensional code pattern displayed on the display screen of the display at the contact position, thereby obtaining the coordinate position on the display screen with which the light pen is in contact.
FIG. 1 is a diagram showing a coordinates pattern which is displayed on the display in the coordinates input system.
The coordinates pattern illustrated in FIG. 1 is constructed by a plurality of blocks each showing one coordinate position by 6 dots in the lateral direction and 6 dots in the vertical direction. 6 dots at a left edge and 6 dots at an upper edge of each block are always set into a turn-off state (shown by black painted dots). Each of other dots is set into a turn-on or turn-off state in accordance with the pattern showing its coordinate position.
FIG. 2 is a schematic diagram showing a construction of one block in the coordinates pattern illustrated in FIG. 1.
In FIG. 2, when display data corresponding to each dot is equal to 1, this means that the dot is in the turn-off state. When it is equal to 0, this means that the dot is in the turn-on state. As shown in FIG. 2, therefore, the turn-on and turn-off patterns shown by a dot train of two rows at the upper edge, a dot train of two columns at the left edge, and the dot at the rightmost lower position are common among all blocks. Since all of the dots existing on a boundary line of each block are, consequently, fixed to the turn-off state, as shown in FIG. 1, a lattice-shaped image pattern in which a display region has been divided every block as a whole coordinates pattern is displayed. A dot of α2·β2 shown in FIG. 2 is a dot showing a reference of the coordinates in one block, what is called, a coordinates reference point.
In each block, 15 dots other than the dot to which the fixed display data has been allocated as mentioned above are used to display information showing a relative position of this block in the whole coordinates pattern. Dots X0 to X7 shown in FIG. 2 indicate the X coordinate positions in the block by the turn-on state/turn-off state of each dot. Dots Y0 to Y6 indicate the Y coordinate positions in the block by the turn-on state/turn-off state of each dot.
When the coordinates information is obtained from the coordinates pattern shown in FIG. 1, therefore, the light pen first detects a position of a block boundary dot train in which the turn-off states of 6 dots continue in the vertical direction and the turn-off states of 6 dots continue in the lateral direction on the basis of a photograph image signal obtained by photographing the coordinates pattern. In this process, if the block boundary dot train, that is, a dot train of {β1, α1} to {β1, α6} in FIG. 2 and a dot train of {β2, α1} to {β6, α1} can be detected, the positions of the dots X0 to X7 and the dots Y0 to Y6 shown in FIG. 2 can be specified. The light pen, therefore, simultaneously photographs regions of nine blocks, that is, the regions of (6 dots×3 times) in the vertical direction×(6 dots×3 times) in the lateral direction so that the image signal corresponding to at least one block is always included in the photograph image signal. On the basis of the position of the block boundary dot train detected from the photograph image signal, the light pen extracts the image pattern corresponding to each of the dots X0 to X7 and Y0 to Y6 from the photograph image signal and obtains the coordinate position shown by the image pattern.
In the above method, therefore, in order to allow one block to be always included in the photograph image signal, the signal process as mentioned above has to be executed to the photograph image signal obtained by photographing the regions which are nine times as large as the block. There is, consequently, such a problem that a processing time which is required to read the two-dimensional code pattern is long.    Patent Document 1: Japanese Patent Kokai No. 2002-082763